Preventing water and wind erosion of soil has employed the deposition of usually fibrous material on the soil. The fibrous material may be simply strewn as bagasse, straw, sawdust, excelsior and may be held in place by suitable binders mixed with the material or sprayed on afterward. One frequently seen mulching technique is the spreading of straw which is then retained in position by being sprayed with tar. The straw tends to hold the earth in position against wind and water erosion until vegetation can take root and flourish. The ground is often treated with fertilizers and/or soil conditioners and seeded before the application of the straw and tar.
The large-scale application of straw such as in highway and strip mine restoration requires at least two vehicles, namely one for spreading straw and one for spraying tar, with their drivers and crews. This usually totals five to seven men. In addition, due to the high bulk of the straw, one or two trucks with drivers are required to deliver the straw to the site.
The high cost and high labor involved in the application of straw and the like for the prevention of erosion has encouraged the growth of hydraulic mulching in which a hydraulic mulch forming fibrous material is mixed in a thin slurry with water and is thereupon transferred to the point of application either by being expelled at high velocity from a nozzle or being directly deposited upon the soil. The hydraulic mulch forming material may consist of ground waste paper, mechanically comminuted wood, partially digested or fully digested paper pulp with or without the lignin removed, or the like. The hydraulic mulch forming material may contain binders such as polyacrylonitrile or other types to aid the mulch in forming a cohesive blanket over the ground, or alternatively the mulch may be deposited without binder and thereupon depend upon intimate and complete coverage of the ground to prevent water or wind erosion.
The hydraulic mulch may contain additional materials such as seed, fertilizer, pesticides, and herbicides or sizing to provide waterproofing qualities to the deposited material. These may all be mixed with the water which forms the slurry and be deposited on the ground at the same time. One advantage of depositing seed and fertilizer together with the mulch is that the seed becomes scarified during the mixing and pumping operation which contributes to the likelihood of germination. Another advantage is that they do not have to be applied in a separate operation. Depositing fertilizer and excess water along with the seed provides a favored environment in which the seed can germinate.
The mulch is customarily prepared as a dry granular material packed in suitable containers such as, for example, paper bags containing fifty pounds of the dry material. In the process of preparation of the dry material, depending upon the type of mulch involved, the material is finely divided either by mechanical comminution or chemical digestion. In certain processes, the material is washed to remove chemical or other products and is dried before being packaged.
Coloring material, usually a green dye, is added to the mulch before drying and packaging. The coloring material serves a number of useful purposes during and after application. The color helps the operator spreading the slurry to spread the material evenly. It provides visual metering which the operator can use to see if the material is spread evenly, thoroughly, and to the proper thickness for uniform, high quality turf. The color also provides an aesthetic benefit while germination is taking place. The green mulch mat gives a pleasant almost finished look to a newly seeded area. Some of the coloring materials used lose their color in direct sunlight in a few days to a few weeks. This gradual loss of color is complementary to the increase in color occurring due to the germination and growth of the turf being established.
The dye is added as an aqueous solution during the forming of the fibrous portion of the hydraulic mulching material. As described in U.S. Pat. No. 3,881,278, incorporated herein by reference, vegetable material is defibrated in steam in a defibrator, whereafter it goes to a cyclone for steam removal and then to a drier for removal of water from the fiber. The dyes are added in aqueous solution between the defibrator and the drier, usually by pumping a dilute solution into the fiber discharge pipe on the defibrator machine. The process is, unfortunately, very messy because the dye solution must be handled in concentrated form, be diluted in a large tank and then be pumped and metered into the fiber system. It has been found that mixing and adding the dye is a messy process resulting in a large area around the processing region being stained with the dye. In addition to the mess which is encountered, the addition of the dye in a dilute medium adds undesirable water to the fiber which must then be driven off in the drier. The additional energy required for this drying is highly undesirable from both cost and fuel conservation points of view. Furthermore, most dyes commonly used in this operation are heat sensitive and therefore have a tendency to lose some of their color through fading during the drying process. To compensate, additional dye must be added to the material. This also results in extra cost.